Ferric silicate

Several silicates containing ferric iron are known in a natural state, chief among which are Anthosiderite, 2Fe₂O₃.9SiO₂. 2H₂O; Cronstedtite, 3FeO.Fe₂O₃.2SiO₂.3H₂O; Hisingerite, 4Fe₂O₃.9SiO₂. 18H₂O; and Nontronite, Fe₂O₃.3SiO₂.5H₂O. A sodium ferric metasilicate occurs as Crocidolite, 2NaFe^•••(SiO₃)₂.Fe^••SiO₃.Na₂SiO₃.